Revenue - Disaggregate of Revenue by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Revenue	$ 128,048	$ 184,673	$ 248,854	$ 354,952
Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	84,742		166,422
Customer Devices [Member]
Disaggregation Of Revenue [Line Items]
Revenue	34,560	33,833	64,661	70,101
Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	8,746	12,201	17,771	26,069
Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	115,063	155,543	220,316	299,140
Network Solutions [Member] | Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	75,222		144,607
Network Solutions [Member] | Customer Devices [Member]
Disaggregation Of Revenue [Line Items]
Revenue	33,306		62,083
Network Solutions [Member] | Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	6,535		13,626
Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue	12,985	$ 29,130	28,538	$ 55,812
Services & Support [Member] | Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	9,520		21,815
Services & Support [Member] | Customer Devices [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,254		2,578
Services & Support [Member] | Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	$ 2,211		$ 4,145